Effects of iodoamphenicol on ribosome assembly in two strains of Escherichia coli.

When the growth of Escherichia coli strain 15TP was inhibited by iodoamphenicol, three 'iodoamphenicol particles' accumulated with sedimentation coefficients of 25S, 33S and 45S. The 25S and 33S particles differ in sedimentation properties from equivalent ribosome precursor particles detected during pulse-labelling of exponentially growing cells. Inhibition of a mutant, strain 15-28 (defective in ribosome assembly), by iodoamphenicol resulted in the accumulation of 38S iodoamphenicol particles that are different from the particles made by the parent. The results support the contention that assembly of 50S ribosomal subunits by the mutant is altered at an early stage.